Process of making hydrocyanic acid from crude cyanides



May I, 1928.

' G. H. BUCHANAN PROCESS OF MAKING HYDROCYANIC ACID FRCBM CRUDE CYANIDES Filed March 25, 1924 I lb vacuum am w Wa Q) Wateror 01 M11301, GIiBucIzanan mama to, 1, 1928.

GU11 BUM I NEW JERSEY, A88IGNOB T0 AMERICAN CYANAm as, o comm, or m Yonx, 1t. Y., a conrona'rron or arms.

m 0! m6 maocramc ACID FED! CRUDE CYLHIDKS.

was fled m 25,

This invention relates to a process of mak- Referring to the accom ying forming a part of this specification m which the is a diagrammatic sectional view of one form of apparatus suitable for carryout this invention, 1 indicates a geuerab ing vessel, 2 a pipe joined to said vessel 4 an absorbing unit containing an absorbm solution 8, 3 a pipe joined, to vessel 1 an 20 to unit 4 and dipping below the surface of absorbing solution 8, 5 a pi joined to unit 4, 6 a water jacket for vesse 1, 7 an agitator in said vessel 1, 11 a valve in pipe 3, 13 a 25 pipe joined to pipe 3 and containing valve In order that the invention may be more clearl understood it is said :--In the processes heretofore pro for the production of hydrocyanic aci from'the well known cyamdes of commerce, it has been customary to treat said cyanides with an acid and thereby form a solution of hydrocyanic acid from which the desired hydrocyanic acid is recovered by distillation. In a co-pending a plication entitled Process of recovering lEydrocyanic acid filed by Guy H. Buchanan and G. B. Winner, on the 25th day of March, 1924, Serial No. 701,741, there is also disclosed a method whereby hydro cyanic acid ma be produced by treating an alkaline earth metal cyanide with water va r.

n this invention, on the other hand, there is disclosed a process whereby a crude anide compound such as is derived from lune nitrogen may be treated with water in the lliglid state and hydrocyanic acid re- COVE This said impure cyanide may be made,

for example, by fusing lime nitro common salt, and calcium carbide toge er in an electric furnace to produce a mixture of sodium 1 nd calcium cyanides. The reportions in the charge may vary de g on 5 the desired concentration of the cyanogen um. Serial lo. 701342.

in the resulting roduct, For example, a standard grade 0' thissaid impure cyanide contains lo-26 per cent cyanogen probably largely in the fame of calcium cyanide. Also, it contains free lime, calcium carbide, on calcium chloride, sodium chloride, carbon and other impurities in quantities dependingeulpon the materials from which it is noduc and on the particular process It is well known in the art that solutions 08 of alkaline earth metal cysnides'are unstable and decompose to form hydrocyanic acid and the so-callcd well known azulmic acid com uuds, the azulmic comfpounds pl'i need by decomposition o a portion 0 I. the hydrocvsnic acid. But the hydrocyanic acid thus formed usually esca and there is left behind only the azuhmc acid bodies and a precipitate composed of an alkaline earth metal hydroxide.

The relative amounts of hydrrofianic acid and of the azulmic bodies need has formerly been considered to de mi solel upon the concentration of the e ea metal cyanide solution, and the statement is frequently made that solutions of calcium cyanide, for example, will decompose almost completely with the production .of azulmic bodies if such solutions are of a concentration greater than 15%.

I have discovered, however, that azulmic bodies are not i'ormed in appreciable quantities provided the hydrocyanic acid is re moved from the mixtures or solutions as rapidly as it is formed. An explanation of the formation of the azulmic bodies is believed to be as follows: The alkali earth metal cyanides are rapidly hydrolyzed in concentrated solutions with formation of hydrocyanic acid, and an alkali earth metal hydroxide. Owing to the fact that the base so liberated is relatively insoluble it is precipitated out and free hydrocyanic aci is left in the solution. I have found that hydrocyanic acid is unstable under such conditions, be'mg rapidly polymerized to form the brown azulmic products above mentioned. Thus an alkaline solution of h drocyanic acid rapidly turns brown an posits lar e flocks of az 'c acid.

I have rther discovered, however, if the hydrocyanic acid be removed from the solution as rapidly as it is formed, azulmic bodies are not produced in substantial amounts and recoveries of hydrocyanic acid 1 from the most out with a current of some may be obtained in excess of of the theoretical. These recoveries may be secured highly concentrated solutions of alkaline earth metal cyanides, and may even be obtained when an alkaline earth metal cyanide such as a crude calcium cya nide, derived from lime nitrogen is merely moistened with Water. To produce hydrocyanic acid from such a crude alkaline earth metal cyanide according to my process, it is only necessary to add to the crude cyanide compound an amount of Water in slight excess of that theoretically required to C0111- plete the following reaction:

oncm i-an o ca onnmucs' and ,then to remove the liberated hydrocyanic acid by reducing the pressure over t e mixture, either with or Without the application of external heat, or such hydrocyanic acid may be removed by sweeping it inert gas such as nitrogen or even air.

In carrying out my process, I introduce into the generating vessel 1 a predetermined quantity of the crude calcium cyanide, for example an amount sufiicicnt to lill the generator say one-quarter full. I then close the generator, start the agitator '7 and apply a vacuum to pipe 13, valve 11 being closed, and valve 10 being open. lVhen the system has been evacuated until a vacuum of 25 inches of mercury has been )roduced, I admit Water through pipe 2. he quantity of water admitted Will vary with the size of the charge of crude cyanide. It is preferred to use an amount equal in weight to substantially 60% the weight of the crude cyanide used. I may, however, use as little water as 40% or as much as 200% of the weight of the cyanide charge. In practice it is preferred to add the water slowly governing the rate of addition by the rate of evolution of gases from the generator. I may, also add the water intermittently in portions equa to approximately one-tenth of the on tire amount used. During the addition I prefer to maintain the water in jacket 6 at a temperature which does not exceed 60 C. When all the Water has been added. I raise the temperature of the Water in jacket 6 to the boiling point, and maintain a vacuum of say 25 inches of mercury within the tem until all evolution of gas has ceased, in order to recover all of the hydrocyanic acid present. The hydrocyanic acid gas thus produced in the vessel 1 asses out of vessel 1 as fast as it is forme through the pipe 3, and the valve 11 being closed and the valve 10 bein open, it will pass through pine 13 into and through a vacuum pump not s own and into a condensing chamber, not shown, Where it may be liquefied by any suitable means, such as a refrigerating apparatus.

Should it be desired to make sodium cyanide by this process, said hydrocyanic acid gas may be passed into the sodium hydroxide 50- lution 8 by closing valve 10 and opening valve 11, whereupon the pipe 5 may be connected to a vacuum pump not shown.

When I use say 7t excess of Water, I. prefer to add it all at one time, and to maintain the temperature oi the mixture at the boiling point.

By operating in this manner I have re peatedly obtained a 90% recovery of hydrocyanic acid in a comparatively pure form, or an equivalent recovery, in solution of sodium cyanide in the absorber 4.

It will now he clear that I have produced a process whereby a crude alkaline earth metal cyanide compound made from lime nitrogen may be treated with water in such a Way that hydrocyanic acid is formed, said process being adapted to remove the hydrocyanic acid from the reaction zone before said hydrocyanic acid has been decomposed, and to recover said hydrocyanic acid in a suitable manner.

What I claim is 1. The process of producing hydrocyauio acid from a crude cyanide containing an al kali earth metal compound which comprises treating the said cyanide with. water; and removing hydrocyanic acid from the zone of reaction, before any objectionable quantities of azulmic compounds are formed.

2. The process of producing hydrocyanio acid from a, crude cyanide containing an alkali earth metal compound which. consists in treating the said cyanide with water, and removing the hydrocyanic acid from the zone of reaction under a pressure less than that of the atmosphere and before any oh jectionable quantities of azulmic compounds are formed.

3. The process of producing hydrocyanic acid from a crude cyanide containing an alkali earth metal compound which consists in treating the said cyanide with water; removing the hydrocyanic acid thus produced from the zone of reaction. substantially as fast as it is formed; and recovering the same.

4. The process of producing hydrocyanic acid from a crude. cyanide containing an alkali earth metal compound which consists in treating the said cyanide with Water while under a pressure less than that of the atmosphere; maintaining the temperature of the mixture below 60 0.; recovering a portion of the produced hydrocyanic acid; raising the temperature of the mixture to a int above 60 (1; and recovering the remainder of the hydrocyanic acid.

The process at producing hydrocyanic acid from a crude cyanide containing an alkali earth metal compound. which comorises gradually supplying Water to said crude cy- 1" anide; and removing hydrocyanic nt'id from the-zone of the reaction, substantially as fast as it is formed.

6. The process of producing hydrocyanic acid from a crude cyanide containing an alkali earth metal c-on'ipound which cmisiF-tS in gradually supplying watcr to said crudc cyanide; heating thc mixture undci' a pressure less than that of the ;ltlll() 'i\il(,l'2 and l((,'()\' 10 ering the hydrm-yanic acid l'orinwl substantially as .fastas it is evolved.

7. The process of producing hydrocyanic acid from a. crude cyanide containing an alkali earth metal compound which consists in is upplyin water to said crude cyanide; heat,-

ing the mixture. under a reduced pressure and recovering the hy lrocyanic acid formed substantially as fast as it is evolved.

S. The process of producing hydrocyamc acid from a crude cyanide containing an alkali carth inctal compound which consists in supplyin water to said crude cyanide in an amount grcatcr than 40?? of the weight of said cyanide and less than 200% of the weight of the said cyanide; heating the mixture under a reduced pressure; and recovering the hydrocyanic acid thus formed.

In testimony whereof I aflix my signature.

GUY H. BUCHANAN. 

